The need to bond the respective curved or flat planar surfaces of two parts together occurs frequently in many and diverse manufacturing areas, and arises independently of the type of materials involved or the particular application at hand. For example in the case of a Stirling engine, it is desirable to effect a virtually void-free bonding joint between the annular “acceptor” or heat exchanger, of the engine and the upper end of the “heater head” cylinder.
The Stirling engine was developed in England in about 1816 as a safer alternative to the steam engines of the time, and operates by alternately heating and cooling a fixed quantity of a working gas, e.g., air, hydrogen or helium, between two temperature extremes. Over the years, many variations of the Stirling engine have been developed, depending on the particular application at hand, and numerous examples of these may be found in the patent literature, e.g., U.S. Pat. No. 4,055,953 to Nederlof; U.S. Pat. No. 4,381,648 to Balas, Jr.; Pat. No. Re. 30,176 to Beale; and, U.S. Pat No. 4,602,174 to Redlich.
One such variant comprises a single-cylinder, free-piston Stirling engine driving a linear electric alternator. The engine includes a relatively large-volume “displacer” that fits loosely within the engine's single cylinder and functions only to displace the fixed quantity of working gas contained in the cylinder between the “heater head,” or heat-input end of the cylinder, and the heat-output, or heat sink end of the cylinder, during which flow, the working gas is caused to pass through an annular “acceptor,” or heat exchanger, located in the upper end of the heater head of the engine.
Stirling engines have numerous advantages relative to other engine types, including that they can utilize external sources of heat energy that do not require the combustion of a fuel with oxygen, e.g., radioisotopes, such as plutonium, making them particularly suitable for electrical power generation applications in deep space probes. However, due to their particular nature, Stirling engines also include certain drawbacks, among which is that they require both input and output heat exchangers, the efficiency of which must be optimized with some care to achieve maximum engine effectiveness. For example, the quality of the bond joint between the exterior wall of the annular heat exchanger and the interior wall of the upper end of the heater head of the engine can dramatically affect the heat transfer capability, and thus, the efficiency, of the heat exchanger.
Hence, there is an important need in a wide variety of fields in general for simple, inexpensive methods and apparatus for effecting reliable, void-free bonds between the respective surfaces of two parts, and in particular for effecting a diffusion bonded or brazed joint between the exterior wall of a first annular cylinder, such as a heat exchanger of a Stirling engine, and the interior wall of a concentric second annular cylinder, such as the heater head of such an engine.